Dog vs Human Chromosomes

Chromosomes: Dog vs Human

A domestic dog (Canis familiaris) carries 78 chromosomes, which works out to 39 pairs. We humans (Homo sapiens) get by on 46 chromosomes, or 23 pairs. You can tie the diploid count back to the pairs with 2n = total chromosomes; pairs = 2n / 2. Both species use the same XX/XY system to set sex, but the dog packs its autosomes into a lot more chromosomes, each smaller and acrocentric. That's worth keeping in mind when you're reading a canine cytogenetics report.

Across the tree of life, chromosome counts are all over the map, and they say nothing about how complex an organism is. The mosquito Culex pipiens gets along with just 2n = 6. At the other extreme, the fern Ophioglossum reticulatum climbs to about 2n = 1260, the highest figure recorded in any eukaryote. Genome size is a separate matter. The human genome runs to roughly 3.2 Gb (giga-base-pairs) of DNA and the dog's to about 2.4 Gb, yet the dog still has far more chromosomes, so on average each of its chromosomes is the smaller one.

Applications

Comparing karyotypes matters a great deal in veterinary genetics, in breed-health screening (centric fusions in certain dog breeds, for instance), in evolutionary biology and in teaching the basics of cytogenetics. Reference assemblies like GRCh38 (human) and CanFam4/ROS_Cfam_1.0 (dog) get heavy use in canine cancer research, since a lot of the tumors that arise spontaneously in dogs look like their human counterparts.

FAQ

Does a higher chromosome count mean a more "evolved" species? No. The number you end up with traces back to ancestral fission and fusion events, not to how advanced a creature is. A plant sitting on hundreds of chromosomes is no further along than a mammal with a few dozen.

Why do dogs have so many chromosomes? Somewhere back in the canid line, the karyotype went through several rounds of fission, snapping large chromosomes into smaller acrocentric pieces. The result is the 78-chromosome arrangement you now see in wolves, coyotes and domestic dogs alike.

Can dogs and humans share genes despite different counts? They can, and they do. About 84% of canine genes have a clear human ortholog. The chromosome number isn't the same, but the genes packed inside overlap to a large degree.